This invention relates to a method of insertion of keratoprostheses, and in particular to a method of surgical insertion and placement of a soft hydrogel prosthetic corneal device into the host cornea. The method of the invention provides a greatly improved rate of success for the implantation and retention of the device.
In spite of 50 years of attempts to make a functional artificial cornea (keratoprosthesis) from synthetic polymers, pathological complications following the implantation of these devices, an operation known as prosthokeratoplasty, have prevented an acceptable success rate from being achieved. Despite considerable research, there is therefore still a need in the art to improve the materials and design of keratoprosthesis.
The most devastating complication of prosthokeratoplasty, extrusion of the polymeric keratoprostheses, appears to be facilitated by the lack of biointegration between implant material and host corneal tissue.
In an attempt to overcome this problem, devices with porous skirts have been developed over the last decade. See for example U.S. Pat. No. 4,865,601 (Caldwell and Jacob-LaBarre); No. 4,923,466 (Pintucci); No. 4,932,968 (Caldwell and Jacob-LaBarre); No. 5,108,428 (Capecchi et al.); No. 5,300,115 (Py); No. 5,300,116 (Chirila et al.); No. 5,458,819 (Chirila et al.); No. 5,489,301 (Barber); No. 5,713,956 (Legeais); and No. 5,843,185 (Leon Rolden and Barraquer Granadas), French Patent No. 2,649,605 (Legeais et al.); and Australian Patent No. 650156 (Chirila et al.). After implantation, these devices are substantially incorporated into the host tissue, due to invasion and proliferation of cells into the pores of the annular peripheral zone. The results obtained in human patients using soft, flexible keratoprostheses with porous skirts appear promising, as disclosed in Caldwell, D. R., Transactions of the American Ophthalmological Society, vol. 95, pp. 751-802 (1997); xe2x80x9cThe soft keratoprosthesisxe2x80x9d; Legeais, J. M., Renard, G., Parel, J. M., Savoldelli, M. and Pouliquen, Y., Archives of Ophthalmology, vol. 113, pp. 757-763 (1995): xe2x80x9cKeratoprosthesis with biocolonizable microporous flurocarbon hapticxe2x80x9d; Legeais, J. M. and Renard, G., Biomaterials, vol. 19, pp. 1517-1522 (1988): xe2x80x9cA second generation of artificial cornea (Biokpro II)xe2x80x9d; and Hicks, C. R., Crawford, G. J., Chirila, T. V., Lou, X., Platten, S., Vijayasekaran, S. and Constable, I. J., Proceedings, The 3rd KPro Study Group Meeting, Birmingham, Jun. 24-26, 1999, pp. 9-10 (1999): xe2x80x9cPilot study of the Chirila keratoprosthesis in human patientsxe2x80x9d.
Relatively few types of soft keratoprostheses have been developed to date. A review of the surgical techniques used for implantation of these devices shows that a full-thickness implantation technique, analogous to a standard penetrating keratoplasty, is normally used.
U.S. Pat. No. 4,586,929 by Binder discloses a keratoprosthesis consisting of a rigid optical cylinder screwed into a soft one-piece system composed of a support cylinder and a base plate, both made from poly(2-hydroxyethyl methacrylate) (henceforth designated as PHEMA) hydrogel. The soft portion is implanted according to a full-thickness procedure consisting of the following steps: superficial lamellar keratectomy, trephination, insertion, suturing, and coverage with the detached keratectomized corneal layer. After the trephination of the latter, the rigid optical cylinder is inserted, then sutured and covered with pretibial periosteum and conjunctiva (if available). Alternatively, in severe dry eye cases, the closed eyelid is sutured over the entire corneal surface.
U.S. Pat. No. 4,693,715 discloses a method of implantation of a PHEMA keratoprosthesis which is a conventional full-thickness procedure, similar to penetrating keratoplasty.
U.S. Pat. No. 4,772,283 by White discloses two procedures for the implantation of a soft PHEMA keratoprosthesis comprising a peripheral portion consisting of preserved (and preferably denatured) human connective tissue (cornea, sclera, cartilage etc.): (a) a conventional full-thickness technique, similar to penetrating keratoplasty; and (b) insertion into an intrastromal pocket, without removing corneal tissue or using sutures. The latter technique is suitable only for the surgical correction of refractive errors, as it is ineffective in the restoration of an irreversibly damaged cornea.
U.S. Pat. Nos. 4,865,601 and 4,932,968 by Caldwell and Jacob-LaBarre disclose a keratoprosthesis consisting of a core made of polyurethanes or silicones, joined to a radial multi-pronged skirt made of porous polytetrafluoroethylene, both portions being soft and flexible. The implantation technique is essentially a full-thickness insertion, involving the removal of the corneal button in two stages. The technique includes: central circular trephination of the cornea as deep as the Descemet""s membrane; radial lamellar incision into the stroma as far as the limbus, in which radial tunnel incisions are cut extending into the sclera; placing the cornea between the walls of the central trephined incision; and placement into the tunnel incisions of the remaining skirt extensions. However, for a modified version of this prosthesis, with a polyurethane core, but a double-layered skirt made of porous polyetherurethanes, Py in U.S. Pat. No. 5,300,115 discloses a full-thickness implantation, identical to a standard penetrating keratoplasty, and stipulates it as an advantage over the previous model.
The procedure disclosed by Capecchi et al. in U.S. Pat. No. 5,489,300 for the implantation of a soft keratoprosthesis, consisting of a poly(vinyl alcohol) core and a fibrous polybutylene skirt, is substantially a full-thickness insertion, identical to penetrating keratoplasty.
Our experience with the soft, flexible PHEMA keratoprosthesis disclosed by Chirila et al. in U.S. Pat. Nos. 5,300,116 and 5,458,819 and in Australian. Patent No. 650156, has shown that the full-thickness implantation technique, analogous to a standard penetrating keratoplasty, has significant disadvantages, and may contribute to postoperative complications: See Hicks, C. R., Crawford, G. J., Chirila, T. V., Lou, X., Platten S., Vijayasekaran, S. and Constable, I. J., Proceedings, The 3rd KPro Study Group Meeting, Birmingham, Jun. 24-26, 1999, pp. 9-10 (1999): xe2x80x9cPilot study of the Chirila keratoprosthesis in human patientsxe2x80x9d.
This full-thickness implantation procedure relies upon the conservation of an intact conjunctival flap, which after opening over the optic, must not retract peripherally, nor enlarge centrally, so as to expose the porous skirt. When the available conjunctiva is compromised by pre-existing pathological conditions, this prerequisite is almost impossible to fulfil. Alternative tissue membranes which may be used for this purpose, such as buccal mucosa, are less satisfactory. Additionally, this procedure is dependent upon perfect perioperative and postoperative wound apposition, which is more difficult to achieve and maintain than with donor tissue. Finally, this procedure is also dependent upon a reasonable resistance to tearing of the skirt when sutured, a requirement which is difficult to fulfill, as the soft porous materials of the keratoprosthesis inherently have a low mechanical strength.
The method of insertion into, and placement within, the host cornea is an important aspect of the implantation of soft keratoprostheses. We have now surprisingly found that certain aspects of this method are critical for a successful outcome of the implantation of a soft, flexible keratoprosthesis with a porous skirt.
It is an object of this invention to provide a simple implantation procedure that assures an insertion and placement of the keratoprosthesis which minimises the risk of postoperative complications such as wound leakage and extrusion. Additional advantages of the method of the invention include one or more of the following:
(a) direct suturing of the prosthesis is not required;
(b) close apposition of the prosthetic skirt to stroma is assured;
(c) the use of a conjunctival flap is less critical, and is not essential for achieving a proper biointegration of the prosthetic rim;
(d) a longer time is available for tissue and vascular ingrowth; and
(e) less frequent follow-up and postoperative maintenance is required.
The method is applicable to any soft, flexible keratoprosthetic model with or without a porous skirt, and indeed to any soft, flexible corneal implant. Thus the invention provides a method of implanting a soft, flexible keratoprosthesis in the eye, comprising the steps of:
(a) de-epithelializing the cornea;
(b) making a 360xc2x0-circular peritomy in the conjunctiva;
(c) making a scleral incision up to the half thickness of the sclera, approximately 1 mm posterior to the superior limbus;
(d) dissecting the cornea at half thickness to create a superior semicircular corneal flap;
(e) making an inferior semicircular intrastromal pocket confined within the lamellar bed, the edge, and the anterior cornea, continuous with the plane of the dissection in the superior cornea;
(f) reflecting inferiorly and retracting the superior corneal flap;
(g) making a circular opening through the posterior corneal lamella, overlying the central visual axis;
(h) inserting the keratoprosthesis into the pocket and placing the optic core centred over the posterior corneal opening;
(i) placing the superior corneal flap over the keratoprosthesis;
(j) suturing the scleral incision;
(k) optionally, fashioning a covering flap to cover the entire surface of the globe; and subsequently
(l) making a central opening, through both the conjunctiva and the anterior corneal lamella to expose the optic of the keratoprosthesis.
Preferably the method also includes one or more of the following features:
(a) the scleral incision extends over about 160 to about 180xc2x0;
(b) the edge of the inferior intrastromal pocket is situated at a distance of about 0.5 to about 3 mm from the limbus;
(c) the circular opening through the posterior corneal lamella has a diameter between about 2 and about 5 mm; the period of time between step (j) and step (k) is between about 1 and about 5 months; and
(d) the circular opening through the covering flap and the corneal flap has a diameter between about 2 and about 5 mm.
The covering flap may be fashioned from conjunctival tissue or may alternatively be fashioned from a mucosal graft. Preferably the mucosal graft is tissue from the buccal mucosa.
It will be clearly understood that the method of the invention is applicable to any soft, flexible corneal implant, with or without a skirt.
For the purposes of this specification it will be clearly understood that the word xe2x80x9ccomprisingxe2x80x9d means xe2x80x9cincluding but not limited toxe2x80x9d, and that the word xe2x80x9ccomprisesxe2x80x9d has a corresponding meaning.